A semiconductor device is an active element-including electronic device using electrical characteristics of a semiconductor. Such a semiconductor device has been widely used in an audio device, a communication device, a computer, an electric appliance and the like. Among these, a thin film transistor (hereinafter, also referred to as a “TFT”) has been commonly used as a switching element or a driver circuit which controls driving of a pixel, in an active matrix driving liquid crystal display device. Recently, an increase in size and an improvement in definition of the liquid crystal display device have rapidly proceeded. Therefore, an improvement in performances of the TFT has been strongly needed. Also, a reduction in production costs of the TFT has been desired.
With respect to the configuration of the TFT, a structure in which a base insulating film, a silicon layer, a gate insulating film, and a gate electrode are stacked on a glass substrate and to the silicon layer, a source electrode and a drain electrode are connected, has been known. Further, a TFT including a silicon nitride film as the base insulating film and the gate insulating film has been known (for example, refer to Patent Documents 1 and 2). Recently, in an active matrix driving liquid crystal display device, polysilicon (polycrystalline silicon) has been used as a material for the polysilicon layer, which is preferably used for improving the performances of the TFT. The polysilicon film is more excellent in mobility in comparison to amorphous silicon, and it can be formed as a film by a low-temperature process. According to the low-temperature process, distortion of the glass substrate, caused by a high temperature, can be suppressed. Therefore, a TFT having a fine structure can be produced on the substrate as designed, which is advantageous for an improvement in performances of the TFT. In addition, for sufficient exhibition of the mobility of the polysilicon film, a process of deactivating a grain boundary and a crystal defect by a hydrogenation treatment is needed.
For this need, a technology of forming a hydrogen-containing film on at least one surface of a polysilicon film, and liberating the hydrogen in the hydrogen-containing film, thereby diffusing it into the polysilicon film (for example, refer to Patent Document 3). However, if a TFT is produced by this technology, the liberation of the hydrogen in the hydrogen-containing film needs to be performed at a sufficiently high temperature. Therefore, it becomes difficult to produce the TFT by a low-temperature process. In such a point, this technology has room for improvement.
In addition, an interlayer insulating film is commonly formed on a TFT in order to flatten a substrate surface or protect the TFT. As a method of forming the interlayer insulating film, not only a plasma chemical vapor deposition (CVD) method but also a liquid phase method using a liquid material containing polysilazane is disclosed (for example, refer to Patent Documents 4 and 5).    [Patent Document 1]    Japanese Kokai Publication No. Hei-05-275701    [Patent Document 2]    Japanese Kokai Publication No. Hei-11-163353    [Patent Document 3]    Japanese Kokai Publication No. 2001-93853    [Patent Document 4]    Japanese Kokai Publication No. 2005-203542    [Patent Document 5]    Japanese Kokai Publication No. 2005-93700